- The largest freshwater fish ever recorded was captured last week in Cambodia’s stretch of the Mekong River: a giant freshwater stingray measuring 4 meters (13 feet) from snout to tail and weighing 300 kilograms (661 pounds).
- The discovery occurred in a stretch of the Mekong known for its diversity of freshwater habitats that support crucial fish-spawning grounds and migration corridors and provide refuges for other mega fish species and threatened species, such as Irrawaddy dolphins and giant softshell turtles.
- Local fishers collaborating with researchers to document the area’s underwater life alerted a monitoring team who measured the ray, fitted it with an acoustic tag to learn more about its behavior, and facilitated its release back into the wild.
- Experts say the find emphasizes what’s at stake in the Mekong, a river that’s facing a slew of development threats, including major hydropower dams that have altered the river’s natural flow. “It is a signal to us to protect our rivers and lakes,” they say.
The largest freshwater fish ever recorded was captured in the Mekong River last week by a fisher collaborating with researchers to document the river’s biodiversity in northern Cambodia. The 4-meter (13-foot) endangered giant freshwater stingray (Urogymnus polylepis) was hauled from the river on June 13 before being measured and released back into the wild.
Tipping the scales at nearly 300 kilograms (661 pounds), the leviathan ray surpasses the previous record holder, a 293-kg (646-lb) Mekong giant catfish (Pangasianodon gigas) caught in Thailand in 2005.
Experts say the find emphasizes what’s at stake in the Mekong, a river that’s facing a slew of development threats, including major hydropower dams that have altered the river’s natural flow and exacerbated low river levels due to dry-season droughts in recent years.
“This is an absolutely astonishing discovery, and justifies efforts to better understand the mysteries surrounding this species and the incredible stretch of river where it lives,” Zeb Hogan, a fish biologist and leader of the USAID-funded Wonders of the Mekong project, said in a statement.
The stingray was hooked in Stung Treng province, in a portion of the Mekong known for its diverse underwater habitats and rich potential to support species of both fisheries and conservation importance. The area, which features pools up to 80 m (260 ft) deep, was last month the focus of an expedition led by the Wonders of the Mekong project in collaboration with the Cambodian Fisheries Administration, the Inland Fisheries Research and Development Institute, and international partners.
As part of that expedition, a network of local fishers agreed to report any catches of giant and endangered fish to the project team for study and safe release. Prior to the latest record-breaking find, a group of fishermen last month reeled in a 180-kg (400-lb) female giant stingray in the same stretch of river.
“These successful releases highlight this site as a stingray hotspot and illustrate [the] importance of partnerships with local communities,” Chea Seila, program manager for Wonders of the Mekong, said in a statement. “Together, we all have an important role to play in fisheries monitoring and conservation.”
In addition to freshwater stingrays, scientists believe this part of the Mekong is a crucial dry-season refuge for other mega fish, including critically endangered Mekong giant catfish and giant barb (Catlocarpio siamensis). The area is also pivotal for the food security and livelihoods of communities in Cambodia and neighboring countries. Fish-spawning grounds and migration corridors make this stretch of the river a natural powerhouse of fish production, generating up to 200 billion fish annually, according to Hogan.
“We now know that this area is critically important,” Hogan added, “not only is it home to the world’s largest freshwater fish, it is also the only place on Earth where a unique assortment of incredibly vulnerable aquatic megafauna — from Irrawaddy dolphin, to giant softshell turtles, to stingray — occur together.”
Categorized as endangered on the IUCN Red List, freshwater stingray numbers are plummeting across their range from rivers in eastern India to Borneo due to declining habitat quality and overexploitation. They spend their entire lives in freshwater, in contrast to marine fish or those that migrate between fresh and saltwater environments like the beluga sturgeon (Huso huso), which can reportedly attain a weight in excess of 1,500 kg (3,500 lbs).
The researchers fitted the ray with an acoustic tag that will enable them to track its movements among the rich assortment of underwater habitats in this area: deep pools, flowing channels, flooded forests, sandbars, and rocky outcrops. By identifying important stingray hangouts, the team will be able to work with communities and authorities to establish any necessary additional protections for the species.
In response to the record-breaking discovery, Poum Sotha, director-general of Cambodia’s Fisheries Administration, said the country has a “special opportunity” to protect the species and its core habitat. He added that efforts will be made to establish a conservation action plan for the species and to boost safeguards for the Mekong, its wildlife, and the communities that rely on its fisheries.
According to Hogan, finding such a colossal specimen is momentous at a time when most giant freshwater fish species are staring extinction in the face. In 2020, the Chinese paddlefish (Psephurus gladius), long a contender for the world’s largest freshwater fish, was officially declared extinct. And recent studies indicate that populations of giant freshwater species have plummeted by almost 90% over the past 40 years.
But it’s also a rare sign of hope, Hogan said, in a river system contending with intense development pressure. “It is a signal to us to protect our rivers and lakes,” he said. “Large fish are bellwethers of the health of freshwater ecosystems worldwide — the fish are sending us a message and we need to listen to it.”
Banner image: Fishers, researchers and fisheries officials prepare to release the giant freshwater stingray into the Mekong River. Image courtesy of Chhut Chheana / Wonders of the Mekong
He, F., Zarfl, C., Bremerich, V., David, J. N., Hogan, Z., Kalinkat, G., … Jähnig, S. C. (2019). The global decline of freshwater megafauna. Global Change Biology, 25(11), 3883-3892. doi:10.1111/gcb.14753
Carolyn Cowan is a staff writer for Mongabay. Follow her on Twitter @CarolynCowan11
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